1. Field of the Invention
The field of art to which this invention pertains is the solid bed adsorptive separation of glucose and mannose. The process employs an adsorbent, a sulfonated crosslinked styrene-divinylbenzene resins to selectively adsorb mannose from a mixture of glucose and mannose. The ion exchange resins are used in the form of a calcium-ammonium exchanged ion exchange mixture.
Mannose can be prepared in several ways, but usually the product is mixed with glucose. According to Bilik (Chem. Zvesti, 26, pp 183-6 (1972)), mannose may be epimerized catalytically to glucose in 25% yield. U.S. Pat. No. 4,029,878 discloses a catalytic epimerization process in which greater yields can be obtained. L-mannose is produced, along with L-glucose, from L-arabinose by cyanide addition and hydrogenation, according to Arena et al. U.S. Pat. No. 4,581,447. Using L-aribinose at 95% purity or greater, a mixture of L-glucose and L-mannose is produced in almost a 2:1 ratio with about 1% arabinose as an impurity. L-arabinose is one of the few L-sugars available freely in nature, such as from sugar beet pulp and rice hulls. The L-sugars have become more important in recent years, with the greater attention to caloric intake, due to the potentially non-metabolizing property of some of the L-derivatives, particularly L-sucrose, L-glucose and L-fructose. Thus, L-sugars are potentially commercially as important as D-sugars, and it is intended to refer to both herein. According to U.S. Pat. No. 4,516,566, L-arabinose may be obtained from different sources of cellulose, e.g., beet pulp, wood, along with other saccharides in the product mixtures depending upon the source of cellulose (U.S. Pat. No. 4,516,566 at column 1, lines 53-58). Further, U.S. Pat. No. 4,440,885 discloses two other methods for deriving L-glucose and L-mannose from L-arabinose: The Sowden-Fischer conversion (J.A.C.S. Vol. 69 (1947) pp 1963-65) and the Kiliani-Fischer synthesis (Organic Chemistry, Morrison and Boyd (3rd. Ed. 1973) pp 1078-9).
2. Description of the Prior Art
It is known from Sherman et al. U.S. Pat. No. 4,471,114 that mannose and glucose can be separated from a solution of the same by selective adsorption on certain cation-exchanged type X or type Y zeolitic molecular sieves. Specifically, Ba-exchanged X- or Y-type and Sr-, Na- and Ca-exchanged Y-type zeolites will selectively adsorb mannose thereon. The nonadsorbed portion is removed from contact with the zeolite. The mannose can be desorbed from the zeolite with a desorbent and recovered.
It is also known from Brit. Pat. No. 1,540,556 (I.C.I.) to separate mannose from glucose by adsorption with a cationic exchange resin, such as Amberlite XE 200, in calcium form. It has been reported, however, that a two-stage separation, using the identical column in each stage, is required to produce a 98% mannose product. However, good separation can't be obtained in a simple column without reflux. Such a process is inefficient and prohibitively expensive.